This invention relates to flexible electro-optic displays, in particular to matrix displays built from two sets of fibers.
An electro-optic display is a device designed to change its optical behavior in response to an applied electric or magnetic field. Such a display usually comprises a plurality of display elements or pixels including an electro-optically active (EOA) substance, organized in a matrix or other pattern. Hereinafter, xe2x80x9cEOA substancexe2x80x9d is meant to denote any substance capable of changing its optic properties such as color, transparency, reflectivity, etc., or capable of emitting light, in response to changes of applied electric or electromagnetic field, and thereby suitable for displaying images. Flexible electro-optic displays may be made on flexible polymer films, where the EOA substance and patterns of electrodes are laid in thin layers over a polymer substrate, or may be built of a plurality of flexible filaments or strips, each having EOA layer, conductive layers, carrying layers, etc.
U.S. Pat. No. 5,962,967 and U.S. Pat. No. 6,072,619 disclose a display made of two sets of fibers arranged in a two-dimensional array. Each fiber includes a longitudinal conductor, and the fibers of at least one set are coated with light-emitting or other EOA substance. A display element (pixel) is formed at each junction where a fiber of one set transverses a fiber of the other set. The two-dimensional array may be formed by overlapping fibers of one set with the fibers of the other set, but preferably and advantageously the two sets of fibers are interlocked in a woven arrangement. Fibers may have round or flat cross-section. The manufacture process of fibers does not pose limitations to their length and, using known weaving techniques, flexible displays of large sizes may be produced. Woven displays do not need patterning (printing) of electrodes or of EOA substance, since the matrix structure with quite uniform pixel spacing is inherent in the nature of the textile fabric. Woven displays are also more flexible and robust than integral film displays.
However, the area of the display element, which is formed by the zone of electro-optical activity (EOA zone) at the junction of two fibers, is limited by the contact zone area of the two fibers or by the overlapping area of the conductive wires or layers in these fibers. Also, conductive wires normally used in such fibers are not transparent and they obscure the EOA zone. As a result, a relatively small quantity of the EOA substance, and a relatively small part of each fiber used in the woven display, may actually be engaged in producing an optical image on the display.
The present invention is concerned with an electro-optic display material comprising a first and a second set of fibers, each fiber having a longitudinal conductive element, the two sets forming a matrix structure of junctions, which structure further comprises an EOA substance at least partially coating the fibers of the first set, and a transparent or translucent conductive layer covering the EOA substance and having electric contact with the fibers of the second set at contact zones in the vicinity of said junctions. The fibers of the two sets are preferably interlocked in woven arrangement, and they can include conductive elements of any structure or have the form of flat strips or tapes. The introduction of the conductive layer over the EOA substance allows to obtain EOA zones and display elements of larger area than the area of a contact zone area between two fibers known in the prior art. The enlarged display elements may be obtained in different ways, according to different aspects of the present invention.
According to a first aspect of the invention, the conductivity of the transparent conductive layer is limited to a predetermined value thereby defining, in the vicinity of each contact zone, an EOA zone constituting a display element.
In one embodiment, the conductivity is selected so as to provide a display element at each junction while avoiding overlapping of adjacent display elements. In an alternative embodiment, the fibers of the two sets are arranged in groups, the space between adjacent groups being larger than the space between fibers within a group. The conductivity of the conductive layer is selected so as to allow the overlapping of adjacent display elements associated with fibers within a group but to prevent overlapping of display elements across adjacent groups, thereby forming a clustered display element over the intersection of a group of first set fibers with a group of second set fibers.
In accordance with a second aspect of the present invention, the transparent conductive layer is laid over the matrix structure in separated spots, each spot overlaying at least one junction and defining an EOA activity zone constituting a display element. Preferably, each spot overlays a plurality of contact zones between the conductive layer and the fibers of the second set thereby forming a clustered display element. The spots may have a rectangular shape to form another matrix over the initial matrix structure, or they may have any other shape and may form any desired pattern. The EOA substance also may be laid over the matrix structure in spots which are separated from each other and/or have different optical properties, thereby forming a visible image.
In accordance with a third aspect of the present invention, the transparent conductive layer is laid over the fibers of the first set in the form of separated sections, each section overlaying a plurality of junctions. The sections define EOA zones constituting clustered display elements.
The display material according to the above three aspects of the present invention may be produced from fibers coated with EOA substance, arranged in a matrix structure and then coated with a transparent conductive layer. Also, fibers may be first coated with EOA substance and a conductive layer thereabove, and then arranged in a matrix structure.
The display materials according to the first and second aspects of the present invention may also be produced from a matrix structure comprising a first and a second set of conductive wires, in which the wires of the first set have an insulating layer, by a method including a) covering the matrix structure with a layer of EOA substance so as to leave exposed parts of each wire of the second set; b) covering the matrix structure, over said layer of EOA substance, with at least one transparent or translucent conductive layer, so that the conductive layer is in electric contact with the exposed wires of the second set. This method allows to avoid creating of internal stresses and cracks in the EOA substance and the transparent conductive layer during weaving.
For the purposes of the present disclosure, it should be understood that if one entity is xe2x80x9ccoveringxe2x80x9d another entity, this does not exclude the presence of other entities between the first two. For example, when a layer of EOA substance coves a wire, this wire may have or may not have some protective or insulating layer on its surface. In a similar way, an xe2x80x9celectric contactxe2x80x9d between two objects should be understood as a proximity which allows such propagation of electric field or energy between these objects as necessary for functioning. For example, an alternating electric current may pass through a dielectric material or a gap between the two objects (capacitance electric contact).
The electro-optic display materials of the present invention have all the advantages of the woven flexible displays outlined in the background and additionally enable an extremely efficient controlled utilization of the EOA substance and length of the electro optic fibers invested in the display. In the case of EL display, for example, the material of the present invention allows to produce displays of unlimited size and resolution, enhanced brightness and low power consumption.